An unexpected pattern of distinct weekly periodicities in climatological variables in GermanyStatistical analyses of data from 12 German meteorological stations meeting WMO standards in the period 1991–2005 are presented. These stations represent different local climate conditions in terms of both meteorology and pollution situation. For the average over data of all stations, we identified significant weekly periodicities in many variables such as temperature, daily temperature range, sunshine duration, cloud amount, precipitation, and precipitation frequency. Not only data of stations situated in congested urban areas, but also data of remote stations as e.g. on Mount Zugspitze 2960 m above sea level in the Alps showed significant in-phase weekly cycles. These weekly periodicities cannot be explained completely by local pollution effects or local heat emissions. We tend towards the hypothesis that the anthropogenic weekly emission cycle and the subsequent aerosol cycle interact with the atmospheric dynamics on a larger scale which leads to a forcing of a naturally existing 7-day period among the spectrum of atmospheric periods.

Large contribution of natural aerosols to uncertainty in indirect forcingThe effect of anthropogenic aerosols on cloud droplet concentrations and radiative properties is the source of one of the largest uncertainties in the radiative forcing of climate over the industrial period. This uncertainty affects our ability to estimate how sensitive the climate is to greenhouse gas emissions. Here we perform a sensitivity analysis on a global model to quantify the uncertainty in cloud radiative forcing over the industrial period caused by uncertainties in aerosol emissions and processes. Our results show that 45 per cent of the variance of aerosol forcing since about 1750 arises from uncertainties in natural emissions of volcanic sulphur dioxide, marine dimethylsulphide, biogenic volatile organic carbon, biomass burning and sea spray. Only 34 per cent of the variance is associated with anthropogenic emissions. The results point to the importance of understanding pristine pre-industrial-like environments, with natural aerosols only, and suggest that improved measurements and evaluation of simulated aerosols in polluted present-day conditions will not necessarily result in commensurate reductions in the uncertainty of forcing estimates.

Climate change scientists must turn their attention to clean skiesNatural aerosols, such as emissions from volcanoes or plants, may contribute more uncertainty than previously thought to estimates of how the climate might respond to greenhouse gas emissions. An international team of researchers, led by the University of Leeds, has shown that the effect of aerosols on the climate since industrialisation depends strongly on what the atmosphere was like before pollution – when aerosols were produced only from natural emissions. The research was published in the journal Nature. Professor Ken Carslaw, from the School of Earth and Environment at the University of Leeds and lead author of the study, said: “We have shown that our poor knowledge of aerosols prior to the industrial revolution dominates the uncertainty in how aerosols have affected clouds and climate.” “In order to better understand climate change, we need to turn our attention towards understanding very clean regions of the atmosphere – as might have existed in the mid-1700s. Such regions are incredibly rare now, but we are looking for them.” […] “Our results provide a clear path for scientists to reduce the uncertainty in aerosol effects on climate because we have been able to rank the causes for the uncertainty,” concludes Professor Carslaw.